Space is a rocky place. The biggest space rocks are asteroids. Asteroids are made up of rock and iron like the four planets closest to our sun. They are different from comets, which are mostly rock and ice. Comets have tails. Asteroids are more like planets and moons. Scientists often call asteroids minor planets.

Some asteroids even have moons. When the Galileo spacecraft flew past asteroid Ida in 1993, scientists were surprised to find it had a little buddy. They named the tiny moon Dactyl.

Most asteroids orbit the sun between Mars and Jupiter. This area is called the asteroid belt. There are millions of asteroids -- and one dwarf planet, Ceres.

Ceres was the first thing discovered in the asteroid belt, probably because it was the easiest to see. It is about 600 miles (960 km) around. This is way smaller than our Moon, which is 2,159 miles (3,475 km) around, but still pretty big. Asteroids are not easy to spot because they often look like very dark blobs against the darkness of outer space.